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Show 56 Michelle Williams college of mines & earth sciences The Green River Formation is a widespread Early Eocene (55-48 million years ago) lacustrine (ancient lake) sedimentary rock deposit well known for its fossil fish and plants. This formation records a system of three major ancient lakes: Lake Gosiute , Lake Uinta, and Fossil Lake, all of which had warm temperate to sub-tropical climatic conditions similar to the modern southern Atlantic regions of the North America. Fossil Lake was the smallest and shortest-lived of the lakes, but preserves most of the fossil vertebrates from the formation, particularly in the Fossil Butte Member. The upper units of Fossil Lake demonstrate it became a hypersaline environment in the center of the lake with few freshwater conditions near the shore. These conditions preserved fossil fish in ghost-like halos, rather than in the higher-fidelity usually associated with Green River fossils. I will use petrographic, sedimentologic, and stratigraphic information to investigate the paleoenvironment and taphonomy of this hypersaline time, and compare it to the main fossil-bearing layers which appear to have been deposited in a deeper freshwater phase. These records will then be com-pared to discern what patterns control the preservation and abundance of fossil preservation. Examina-tion of key fossil-preserving beds using QEMSCAN analysis of rock thin sections and x-ray diffraction allow quantitative and detailed examination of the petrology of these units. These methods will help better characterize of makeup and geochemistry of the sediments preserving fossils in the Green River Forma-tion. This information will provide a clearer picture of how this unusual fossil ecosystem is preserved, what conditions control the depositional environment of the lake, and how these environments changed over time. FISH TAPHONOMY AND LAKE PALEOENVIRONMENTS OF THE GREEN RIVER FORMATION, FOSSIL LAKE, WYOMING Michelle Williams (Randall Irmis, Mark Loewen) Department of Geology and Geophysics University of Utah UNDERGRADUATE RESEARCH ABSTRACTS Randall Irmis Mark Loewen |